Turtle in a Tunnel

Satellite transmitters glued to the backs of sea turtles have been used to track turtle migrations for several years now.

But until wind tunnel tests were performed on this 18-inch-long plaster model of a green sea turtle, researchers never knew how their transmitters affected the turtles. Mechanical engineers Kennard Watson of the Naval Surface Warfare Center in Panama City, Florida, and Robert Granger of the Naval Academy in Annapolis, Maryland, used the carcass of a juvenile turtle that had washed up on a Florida beach as a mold. They anchored a foam model of a satellite transmitter to the turtle's back with modeling clay. Wind-tunnel tests showed that the transmitter increases the drag on the turtle by up to 30 percent, causing it to swim some 11 percent slower. To maintain normal speeds, the turtle must expend up to 27 percent more energy. "The transmitters certainly aren't killing the turtles, but they probably do stress them and alter their behavior," says Watson, which is exactly what biologists would like to avoid. To reduce that stress, Watson recommends a more hydrodynamic transmitter design. "We suggest that researchers get away from the boxy transmitter and make one with a teardrop shape."